Calculation of tsunami horizontal velocity field from tsunami magnetic field
An new dataset for tsunami early warning
Lin Zhiheng¹, Toh Hiroaki²

データ同化研究支援センター¹Center for Data Assimilation Research and Applications, Joint Support-Center for Data Science Research, The Institute of Statistical Mathematics, Tokyo, Japan²Data Analysis Center for Geomagnetism and Space Magnetism, Kyoto University, Kyoto, Japan

Introduction

Contents

Tsunami can generates induced magnetic field·Derivation of the equation for estimatingtsunami horizontal velocity fields fromtsunami magnetic fields.

Tsunami early warning process

Earth's magnetic field

予

海底電位磁力計

Induced current
Induced magnetic field

Exact result (Fy = 14361 nT, 2010 Chile tsunami)

Uniform Earth's magnetic fieldve (m/s)

0.005

tsunami frequency
tsunami direction_Surface

Seawater: 3.3
S/m_Surface

The Approximate Equation&Approximate result (Fy = 0 nT)

00−0.005_Surface

Seafloor: 0.01
S/m_Surface

SOC8−0.005
0.005
vn (m/s)Unknown！
Air: 0 S/m

Data

Accuracy examinations

Linear dispersive wave equations:

Tsunami prediction
and alert

This study can provide tsunami velocity field
for tsunami early warning.

Seafloor

Methods

The Exact Equation

Tsunami data observation
and analysis

Tsunami generation

29 Feb 2024

Tsunami-induced magnetic field

波Tsunami

Presented at the 第4回ROIS-DS成果報告�, ISM, Tokyo, Japan

Tsunami velocity field津

津波磁場·Comparisons of estimated tsunami horizontal
velocity fields from simulation andobservation of tsunami magnetic fields withsimulation results.

Maxwell's equation:

測

16:00

16:30

17:00

17:30

18:00

27 Feb 2010

tsunami frequency

Estimated tsunami horizontal velocities from simulated tsunami magnetic field
by using exact equation and approximate equation

Resultsfor simulation datafor observation dataConclusions

2010 Chiletsunami&·We derived an equation for estimatingtsunami horizontal velocities fromtsunami magnetic fields.

Estimated velocity

Ve Vn·Compared to the simulation, ourestimation equation is very accurate.

Simulated velocity

References
Baba, Toshitaka & Cummins, Phil & Hori, Takane. (2005). Compound fault rupture during the 2004 off the Kii Peninsula earthquake(M7. 4) inferred from highly resolved coseismic sea-surface deformation. LETTER Earth Planets Space. 57. 167-172. https://doi.org/10.1186/BF03351810
Baba, T., Allgeyer, S., Hossen, J., Cummins, P. R., Tsushima, H., Imai, K., et al. (2017). Accurate numerical simulation of the far-fieldtsunami caused by the 2011 Tohoku earthquake, including the effects of Boussinesq dispersion, seawater density stratification,
elastic loading, and gravitational potential change. Ocean Model., 111, 46–54. https://doi.org/10.1016/j.ocemod.2017.01.002
Minami, T., Toh, H., Ichihara, H., & Kawashima, I. (2017). Three-dimensional time domain simulation of tsunamigenerated
electromagnetic �elds: Application to the 2011 Tohoku earthquake tsunami. Journal of Geophysical Research: Solid Earth, 122,9559–9579. https://doi.org/10.1002/2017JB014839
Minami, T., Schnepf, N.R. & Toh, H. (2021). Tsunami-generated magnetic fields have primary and secondary arrivals like seismicwaves. Scientific Reports, 11, 2287. https://doi.org/10.1038/s41598-021-81820-5
Suetsugu, Daisuke & Shiobara, Hajime & Sugioka, Hiroko & Ito, Aki & Isse, Takehi & Kasaya, Takafumi & Tada, Noriko & Baba,Kiyoshi & Abe, Natsue & Hamano, Yozo & Tarits, Pascal & Barriot, Jean-Pierre & Reymond, Dominique. (2012). TIARES Project– Tomographic investigation by seafloor array experiment for the Society hotspot. Earth Planets and Space. 64. i-iv. 10.5047/
eps.201.11.002.

TIARES area

Acknowledgments
Estimated tsunami velocity fields from the simulated tsunami magnetic fields VS

Simulated tsunami velocity fields

Estimated tsunami velocity fields from the observed tsunami magnetic fields VSSimulated tsunami velocity fields

We thank Dr. K. Baba at U. Tokyo for providing the observed magnetic field data. We also appreciate Prof. T. Baba at Tokushima
University for making the JAGURS code available and inverting the tsunami source model for us. Finally, we are grateful to Dr. S.
Fujita, Dr. G. Ueno, and Dr. S. Nakano at ISM for discussion on this study.